Wafer polishing apparatus

ABSTRACT

A wafer polishing apparatus includes a wafer mount mounting thereon a wafer for rotation, a pair of bell-shaped buff units opposing each other and rotated to polish the periphery of the wafer. The buff units each have an edge-surface polishing section having a shape adapted to half the edge surface of the wafer periphery as divided in the thickness direction of the wafer, and a notch polishing section having a shape corresponding to half the edge surface of a notch of the wafer as divided in the thickness direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wafer polishing apparatus and, moreparticularly, to a wafer polishing apparatus that polishes a waferperiphery including a notch.

2. Description of the Related Art

In manufacture of a semiconductor device, a variety of films, such as anoxide film, a nitride film, a carbide film, a polycrystalline film or ametallic film are deposited on a semiconductor wafer (hereinafter,referred to merely as “wafer”) configuring the substrate of thesemiconductor device. The above films are deposited inadvertently at theperiphery or edge surface of the wafer. The portion of the filmdeposited on the edge surface of the wafer is easily peeled-off from thewafer to generate undesirable particles. The undesirable particlesgenerated in the process for manufacturing the semiconductor device maybe adhered onto a device area formed on the wafer surface to cause ashort-circuit failure between interconnect lines, for example, resultingin degradation of the product yield in the manufacture of thesemiconductor device. Therefore, after the filming process, the, edgesurface of the wafer is polished to remove the film formed on the edgesurface.

FIG. 6A shows a typical wafer in a top plan view. A V-character shapedor circular-arc-shaped notch 62 is formed on an edge portion of thewafer by cutting the wafer 60 from the circumference of the wafer 60toward the inner circumference thereof In manufacture of thesemiconductor chips on the wafer, the notch 62 is used as a referencepoint for detecting the position or direction of the wafer 60. Apeel-off of the film deposited on the, wafer periphery may easily occur,especially at the notch 62. Therefore, a polishing process for the waferperiphery should be applied onto the circumferential edge surface of thewafer including the notch 62. FIG. 6B is a sectional view taken alongline b-b in FIG. 6A. As shown in FIG. 6B, the wafer 60 has a symmetricstructure in the thickness direction thereof, and has a bulge where thecentral portion of the wafer 60 in the thickness direction moderatelyprotrudes from the top-side and bottom-side portions of the waferperiphery 61 including the notch 62.

Patent Publication JP-2000-317790A describes a conventional waferpolishing apparatus that polishes the wafer periphery including thenotch 62. FIG. 7 is a side view showing the configuration of the waferpolishing apparatus described in this publication. The wafer polishingapparatus, generally designated at numeral 70, includes a wafer mount 71that mounts thereon a wafer and rotates the wafer, an edge-surfacepolishing device 72 that polishes the edge surface of the waferperiphery 61, and a notch polishing device 73 that polishes the edgesurface of the notch 62 of the wafer 60. The wafer mount 71 includes awafer suction pad 74 that fixes the wafer 60 by suction, a waferrotation unit 75 that rotates the wafer suction pad 74, and a wafertilting unit 76 that tilts the wafer rotation unit 75.

The edge-surface polishing device 72 has a cylindrical abrasive cloth(buff) 78 that rotates about the rotational axis 77 which isperpendicular to the plane including the wafer 60. A groove 79 having across section corresponding to the section of the wafer periphery 61 isformed on the surface of the buff unit 78. In a process of polishing thewafer periphery 61, the wafer 60 and buff unit 78 are rotated atrespective predetermined rotational speeds, and the buff unit 78 ispressed against the wafer periphery 61 at the groove 79 thereof, whileabrasive slurry is supplied onto the groove 79, to polish the wafer 60along the circumferential direction thereof. In this state, the wafer 60is tilted with respect to the groove 79 by the operation of the wafertilting unit 76, to thereby polish the wafer periphery 61 along thethickness direction from the top-side edge toward the bottom-side edgeof the wafer periphery.

The notch polishing device 73 has a disk-shaped buff unit 80 thatrotates in a vertical plane, which extends perpendicular to the planeincluding the wafer 60 and in the radial direction of the wafer 60. Thebuff unit 80 has an edge portion adapted to the shape of the notch 62.In a process of polishing the notch 62, while the slurry is supplied,the buff unit 80 is rotated and pressed against the notch 62 withoutrotating the wafer 60. In this state, the wafer 60 is tilted by theoperation of the wafer tilting unit 76 to thereby polish the notch 62along the thickness direction thereof from the top-side edge to thebottom-side edge of the wafer.

By reducing the occupied area of individual semiconductor manufacturingapparatuses used for the process for manufacturing the semiconductordevice, it is possible to reduce the time length required fortransferring the wafer 60 to thereby improve the production efficiency.However, in the case of the conventional wafer polishing apparatus asdescribed above, the edge-surface polishing device 72 that polishes thewafer periphery 61 and notch polishing device 73 that polishes the notch62 have to be separately arranged in the area adjacent to the wafer 60,with the result that the size of the entire apparatus is inevitablyincreased. Thus, it is difficult to reduce the, occupied area for thewafer polishing apparatus in the conventional technique.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention toprovide a wafer polishing apparatus that polishes the wafer peripheryincluding a notch thereof and is capable of reducing the occupied areafor the wafer polishing apparatus for improving the productionefficiency.

The present invention provides a wafer polishing apparatus including: awafer mount for mounting thereon a wafer and rotating the wafer about arotational axis; at least one buff unit having a rotational symmetry androtating in a rotational axis parallel to the rotational axis of thewafer mount; and a moving unit for moving the wafer relative to the buffunit, the buff unit including a edge-surface polishing section having ashape adapted to polishing an edge surface of the wafer and a notchpolishing section having a shape adapted to polishing a notch of thewafer.

In accordance with the wafer polishing apparatus of the presentinvention, the buff unit including the edge-surface polishing sectionand the notch polishing section allows the polishing apparatus to have asmaller occupied area. It is to be noted that the moving unit may moveany of the wafer and the buff unit.

The above and other objects, features and advantages of the presentinvention will be more apparent from the following description,referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing the configuration of a waferpolishing apparatus according to an embodiment of the present invention;

FIG. 2 is an exploded perspective view showing the configuration of thebuff unit and buff fixing members shown in FIG. 1;

FIG. 3 is a sectional view of the buff unit taken along the direction inwhich the fitting groove shown in FIG. 2 extends;

FIG. 4 is a flowchart showing the procedure of a wafer polishing processusing the wafer polishing apparatus of FIG. 1;

FIGS. 5A to 5D are side views showing the positional relationshipbetween the wafer and the buff unit during polishing the wafer atrespective positions thereof;

PIG. 6A is a top plan view of a typical wafer, and FIG. 6B is asectional view of the typical wafer taken along line b-b in FIG. 6A; and

FIG. 7 is a side view showing the configuration of a conventional waferpolishing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below in detailwith reference to the accompanying drawings. FIG. 1 is a sectional viewshowing the configuration of a wafer polishing apparatus according to anembodiment of the present invention. The wafer polishing apparatus,generally designated at numeral 10, includes a wafer mount 11 formounting and rotating thereon a wafer 60 in a horizontal plane(XY-plane), and a polishing section 12 including a pair of bell-shapedbuff units 21 a and 21 b opposing each other in the Z-axis direction forpolishing the periphery of the wafer 60. The buff units 21 a and 21 bconfigure a body of the polishing section 12 in the present embodiment.

The wafer mount 11 includes a wafer holding unit that holds the wafer60, a rotation unit that rotates the wafer holding unit about arotational axis 13 extending parallel to the Z-axis, a Z-axis movementunit that moves the wafer holding unit in the Z-axis direction, and anX-axis movement unit that moves the wafer holding unit in the X-axisdirection, i.e., direction from the wafer mount 11 to the polishingsection 12. The wafer holding unit mounts the wafer 60 by utilizing asuction force, and holds the wafer 60 at the bottom surface of the wafer60.

The rotation unit, Z-axis movement unit, and X-axis movement unit aredriven by an adjustable-speed motor, a stepping motor, and an aircylinder, respectively. The X-axis movement unit includes a pressuresensor that detects the pressure in the air cylinder and a pressurecontrol member that controls the pressure in the air cylinder based onthe pressure detected by the pressure sensor. By controlling thepressure in the air cylinder, a pressing force pressing the wafer 60against the buff units 21 a, 21 b in the X-direction can be adjusted.

In the polishing section 12, the pair of buff units 21 a and 21 b aredisposed in a plane symmetry with respect to each other and outside thearea of the wafer 60 in the radial direction thereof. The buff units 21a and 21 b each have a rotational symmetry with respect to therotational axis 14 thereof. The buff units 21 a and 21 b each include abuff body 22 a, 22 b and a buff-body support 23 a, 23 b tat supports thebuff body 22 a, 22 b. The buff body 22 a, 22 b is made of polyurethanefoam shaped by integral molding, and the surface thereof serves as apolishing surface. The buff body 22 a, 22 b has a bell-like, ordome-like shape including a narrow tip portion 25 a, 25 b, a middlecurved portion 24 a, 24 b, and a substantially cylindrical bottom end.The middle curved portion 24 a, 24 b extends from the narrow tip portion25 a, 25 b in a smoothly stepped fashion and has a radius larger thanthe radius of the narrow tip portion 25 a, 25 b and smaller than theradius of the substantially cylindrical bottom end. The substantiallycylindrical bottom end of the buff body 22 a, 22 b supports the middlecurved portion 24 a, 24 b and is supported by the buff-body support 23a) 23 b. The narrow tip portions 25 a, 25 b of both the buff bodies 22 aand 22 b are disposed opposite to each other with an intervention of theplane including the wafer 60.

The middle curved portion 24 a, 24 b of the buff body 22 a, 22 b is usedas an edge polishing section for polishing the periphery of the wafer60, and the narrow tip portion 25 a, 25 b of the buff body 22 a, 22 b isused as a notch polishing section for polishing the notch of he wafer60. The edge polishing section 24 a, 24 b has a shape adapted to theshape of the half portion of the edge of the wafer 60 as divided in thethickness direction. The notch polishing section 25 a, 25 b has a shapeadapted to the half portion of the notch of the wafer 60 as divided inthe thickness direction. The notch polishing section 25 a, 25 b has asmall diameter and is adapted to the top-side or bottom-side edge of thenotch of the wafer.

The buff units 21 a and 21 b are fixed, at the bottom portion of thebuff-body supports 23 a and 23 b, onto the buff fixing members 26 a and26 b. The buff fixing members 26 a and 26 b are rotatably supported by asupporting unit 28 by way of bearings 27 a and 27 b. Further, the bufffixing members 26 a and 26 b are coupled to rotating units 29 a and 29 bthat rotate the buff fixing members 26 a and 26 b, respectively, aboutthe rotational axis 14. The rotating units 29 a and 29 b are configuredby a pulse motor, and control the rotational direction and rotationalspeed of the buff units 21 a and 21 b independently of each other.

Four nozzles 30 for supplying slurry or pure water to the buff units 21a and 21 b are provided to oppose the wafer 60 with an intervention ofthe buff units 21 a and 21 b, extending from and being supported by thesupporting unit 28 of the polishing section 12. The four nozzles 30 arearranged so as to correspond to the edge polishing sections 24 a and 24b and notch polishing sections 25 a and 25 b of the buff units 21 a and21 b. A slurry supply system for supplying slurry, a pure water supplysystem for supplying pure water, and a supply system switching sectionfor switching the supply system to be coupled to the nozzles 30 areprovided in the supporting unit 28.

FIG. 2 is an enlarged perspective view of the buff unit 21 a (and 21 b)and the buff fixing member 26 a (26 b). Formed at the top portion of thebuff fixing members 26 a is a protrusion 43 including a rectangularprism portion 41 having a substantially rectangular solid shape and acylindrical portion 42 having a substantially circular cylindrical shapeand formed on the rectangular prism portion 41 and around the rotationalaxis 14. A fitting grove 44 to be fitted to the protrusion 43 is formedin the bottom portion of the buff-body support 23 a. The rectangularprism portion 41 and part of the fitting portion 44 (rectangular solidslot 47) to be fitted to the rectangular prism portion 41 are formed forpreventing idle running of the buff unit 21 a.

Three screw holes 45 are formed in the buff-body support 23 a. The screwholes 45 penetrate from the surface of the buff-body support 23 a to thefitting groove 44 formed at the center of the buff-body support 23 aalong the radial direction thereof. The three screw holes 45 are formedat an interval of 120° with respect to the rotational axis 14.

After the polishing apparatus is used for polishing a specific number ofwafers or polishing for a specific time length, the surface of the buffbody 22 a, 22 b is clogged with foreign matter such as polishedparticles or has a larger roughness, with the result that the polishingcapability is deteriorated. Therefore, the buff body 22 a, 22 b has tobe replaced with a new one periodically. In the present embodiment,replacement of the buff body 22 a, 22 b can be achieved by replacementof the buff units 21 a and 21 b.

As shown in FIG. 2, when the buff unit 21 a (21 b) is fitted to the bufffixing members 26 a (26 b), positioning is performed such that the sideportion of the fitting groove 44 of the buff opposes the cylindricalportion 42 of the buff fixing members, and buff unit 21 a is movedtoward the buff fixing members 26 a to allow the protrusion 43 to beinserted into the fitting groove 44. After the insertion is completed sothat the rotational axis 14 of the buff unit 21 a is aligned with therotational axis 14 of the buff fixing members 26 a, the buff unit 21 ais pressed against the buff fixing members 26 a along the rotationalaxis 14 to allow the protrusion 43 to be fitted to the fitting groove44.

Thereafter, screws 46 are inserted into the screw holes 45 to press thecylindrical portion 42 for fixing. The reverse procedure may be used toremove the buff unit 21 a (21 b) from the buff fixing members 26 a (26b). According to the above procedure, there is no need to disassembleparts of the polishing section 12 such as the buff fixing member 26 a,26 b when the buff units 21 a and 21 b are replaced with new ones,whereby the replacement of the buff units 21 a and 21 b can be performedefficiently.

FIG. 3 shows a sectional view of the buff unit 21 a (21 b) taken alongthe direction in which the fitting groove 44 shown in FIG. 2 extends.The fitting groove 44 is configured by a rectangular solid slot 47 thatreceives therein the rectangular prism portion 41 of the buff fixingmember 26 a (26 b) and a cylindrical slot 48 that receives therein thecylindrical portion 42 of the buff fixing member 26 a(26 b).

Formed on the surface of the buff-body support 23 a is a protrusion 53including a cylindrical portion 51 having a center aligned with therotational axis 14 and a rectangular prism portion 52 having asubstantially rectangular solid shape that protrudes outward from theside surface of the cylindrical portion 51. A fitting grove 56 includinga cylindrical slot 54 to be fitted to the cylindrical portion 51 and arectangular prism slot 55 to be fitted to the rectangular prism portion52 is formed at the bottom portion of the buff body 22 a. Therectangular prism portion 52 and rectangular prism slot 55 are formedfor preventing idle running of the buff body 22 a.

FIG. 4 is a flowchart showing the procedure of a wafer polishing processusing the wafer polishing apparatus 10 of FIG. 1. The wafer 60 receivedin a wafer cassette is transferred onto the wafer mount 11 by way of awafer transfer system. The wafer mount 11 mounts thereon the wafer 60 bysucking the bottom surface of the wafer 60 to fix the position thereofonto the wafer mount 11 (step S11).

Thereafter, slurry is supplied from the nozzles 30 at a specific flowrate, and buff units 21 a and 21 b are rotated in a predetermined.rotational direction and at a predetermined rotational speed by way ofthe rotating units 29 a and 29 b (step S12). Subsequently, the wafermount 11 moves the wafer 60 in the X-axis direction while rotating thewafer 60 to allow the wafer periphery 61 to be in contact with theedge-surface polishing section 24 b, as shown in FIG. 5A. In this state,the wafer 60 is moved along the contour of the edge-surface polishingsection 24 b in the X-axis and Z-axis directions, and the edge surfaceof the wafer periphery 61 is polished from the top-side edge toward themiddle-portion edge in the thickness direction of the wafer 60 (stepS13).

Thereafter, the wafer mount 11 moves the wafer 60 in the X-axis andZ-axis directions while rotating the wafer 60 to allow the waferperiphery 61 to be in contact with the edge-surface polishing section 24a, as shown in FIG. 5B. In this state, the wafer 60 is moved along thecontour of the edge-surface polishing section 24 a in the X-axis andZ-axis directions, and the edge surface of the wafer periphery 61 ispolished from the bottom-side edge toward the middle-portion edge of thewafer (step S14). The pressing force for pressing the wafer 60 againstthe edge-surface polishing sections 24 a and 24 b can be controlled bythe pressure control member of the X-axis movement unit in steps S13 andS14.

Then, the rotation of the wafer 60 is stopped once, and an opticalposition sensor (not shown) is used to perform positioning of the notch62 by rotating the wafer 60 such that the center of the, notch 62 isaligned with the rotational axis 14 of the buff units 21 a and 21 b(step S15).

Subsequently, the wafer mount 11 moves the wafer 60 in the X-axis andZ-axis directions to allow the notch 62 to be in contact with the notchpolishing section 25 b, as shown in FIG. 5C. In this state the wafer 60is moved in the X-axis and Z-axis directions step by step, and the edgesurface of the notch 62 is polished from the top-side edge toward themiddle-portion edge of the notch 62 in the thickness direction (stepS16).

Thereafter, the wafer mount 11 moves the wafer 60 in the X-axis andZ-axis directions to allow the notch 62 to be in contact with the notchpolishing section 25 a, as shown in FIG. 5D. In this state, the wafer 60is moved the in X-axis and Z-axis directions step by step, and the edgesurface of the notch 62 is polished from the bottom-side edge toward themiddle-portion edge of the notch 62 in the thickness direction (stepS17). The pressing force for pressing the wafer 60 against the notchpolishing sections 25 a and 25 b can be controlled by the pressurecontrol member of the X-axis movement unit in steps S16 and S17.

Subsequently, the supply of slurry from the nozzle 30 is stopped, andthe wafer 60 is moved in the X-axis direction away from the buff units21 a and 21 b. Subsequently, the rotation of the wafer 60 is stopped,and fixation of the wafer 60 by the wafer mount 11 is released (stepS18). Thereafter, the wafer transfer system moves the wafer 60 to awafer cleaning system in the wafer polishing apparatus and performs acleaning treatment to remove the attached slurry (step S19).Subsequently, the wafer 60 is received in the wafer cassette by thewafer transfer system, and a series of processing steps are completed.

After the buff units 21 a and 21 b are released from the wafer 60, purewater is supplied from the nozzles 30 to the surface of the buff units21 a and 21 b until the polishing for the next wafer 60 is started tothereby perform dressing of the surface of the buff units 21 a and 21 b.The procedure shown in FIG. 4 is only an example, and variousmodifications may be made as desired.

In the wafer polishing apparatus 10 according to the present embodiment,the buff units 21 a and 21 b each include the edge polishing section 24a, 24 b having a shape corresponding to the edge surface of the waferperiphery 61 and the notch polishing section 25 a, 25 b having a shapecorresponding to the edge surface of the notch 62. The X-axis movementunit and Z-axis movement unit move the wafer 60 relative to the buffunits 21 a and 21 b, thereby polishing the wafer periphery including thenotch 62 along the edge surface thereof In the conventional polishingapparatus, the edge-polishing device and the notch polishing device areseparately provided in the wafer polishing apparatus, whereby the waferpolishing apparatus has a large occupied area. In contrast, in the waferpolishing apparatus according to the above embodiment the configurationwherein the edge-surface polishing section and notch polishing sectionare provided as an integrated device allows the wafer polishingapparatus to have a smaller occupied area.

Further, in the polishing treatment along the thickness direction of thewafer periphery, the wafer 60 need not be tilted, differently from thecase of the conventional wafer polishing apparatus 70 of FIG. 7. Thiseliminates the need to provide a wafer tilting unit that requires alarge torque, thereby reducing the power dissipation of the wafer-edgepolishing apparatus. Since it is not necessary to separately provide theedge-surface polishing buff and the notch polishing buff and since thepair of buff units 21 a and 21 b have the same design shape, it ispossible to reduce the cost required for replacement of consumablesupplies.

Although the buff unit is configured by the pair of buff units 21 a and21 b in the above embodiment, the polishing section may be configured bya single buff unit so long as the buff unit has an edge-surfacepolishing section having a shape corresponding to the edge surface ofthe wafer periphery 61 and a notch polishing section having a shapecorresponding to the edge surface of the notch 62. Further, the buffbody 22 a, 22 b may be made of rigid urethane resin instead of the foampolyurethane.

Although the present invention has been described based on the preferredembodiment, the configuration of the wafer polishing apparatus accordingto the present invention is not limited to that described in the aboveembodiment, and various modification and alternation may be made withoutdeparting from the spirit and scope of the invention. Thus, any waferpolishing apparatuses obtained by such modification and alternation arealso included in the scope of the invention.

1. A wafer polishing apparatus comprising: a wafer mount for mountingthereon a wafer and rotating the wafer about a rotational axis; at leastone buff unit having a rotational symmetry and rotating in a rotationalaxis parallel to said rotational axis of said wafer mount; and a movingunit for moving the wafer relative to said buff unit, said buff unitincluding a edge-surface polishing section having a shape adapted topolishing an edge surface of the wafer, and a notch polishing sectionhaving a shape adapted to polishing a notch of the wafer.
 2. The waverpolishing apparatus according to claim 1, wherein said at least one buffunit include a pair of buff units disposed in a plane symmetry with eachother.
 3. The wafer polishing apparatus according to claim 2, whereinsaid edge-surface polishing section has a shape adapted to polishinghalf said edge surface of the wafer in the thickness direction thereofand said notch polishing section has a shape adapted to half the surfaceof the notch in the thickness direction thereof.
 4. The wafer polishingapparatus according to claim 1, wherein said moving unit moves the waferin a first direction parallel to said rotational axis of said wafermount and in a second direction normal thereto.
 5. The wafer polishingapparatus according to claim 4, wherein said moving unit includes astepping motor for moving said wafer in said first direction.
 6. Thewafer polishing apparatus according to claim 4, wherein said moving unitincludes a pressing means for pressing the wafer against said buff unitat a controlled pressure.
 7. The wafer polishing apparatus according toclaim 1, wherein said buff unit includes a buff body made ofpolyurethane foam or rigid urethane.
 8. The wafer polishing apparatusaccording to claim 1, further comprising a nozzle, opposing the waferwith an intervention of said buff unit, for supplying slurry onto acontact surface between the wafer and said buff unit.